1. [Field of the invention]
The present invention relates to a flow rate sensor for detecting the flow rate or flow velocity of a fluid and more particularly to a thermo-sensitive type flow rate sensor for favorably detecting an air flow rate flowing into an internal combustion engine used for example in automobiles and the like.
2. [Description of the Prior Art]
As shown in Japanese laid-Open Patent Application (Kokai) No. Hei 10-142020 and U.S. Pat. No. 5,631,416, a thermo-sensitive type flow rate sensor having a sensing element is disclosed. Namely, the thermo-sensitive type flow rate sensor is known in which an exothermic resistor and an thermometric resistor consisting of a platinum thin film serving as the sensing element are evaporated on a silicon substrate by means of a micro-machining technique or they are deposited on the substrate by a sputtering method and the like.
FIGS. 34 and 35 show the structure of the thermo-sensitive type flow rate sensor that is introduced in U.S. Pat. No. 5,631,416.
In FIG. 34, reference numeral 101 is a holder consisting of a measuring pipe conduit 102, a housing portion 103 and a connector-connecting portion 104 that are integrally formed by a resin. This holder 101 is formed in a rectangular shape elongated longitudinally in a direction of a plug axis 105 and inserted from an opening portion 20k of a main conduit 20, the substantially central part of which is provided with the measuring pipe conduit 102. The housing portion 103 is formed a recess 106 on which a casing 107 is mounted.
As shown in FIG. 35, this casing 107 is formed by a plate-shaped support 108 for holding a sensing element 4, and a plate-like base portion 110 having a U-shape in section which are integrally formed by thin plate-like metal material. The sensing element 4 is housed in a housing portion 109 formed on the support 108 and secured by an adhesive agent applied on a bottom face of the housing portion 109.
Also, a control circuit substrate 22 made of ceramic base material is secured to the base portion 110 by an adhesive agent.
As shown in FIG. 34, electric connection of the sensing element 4 with the control circuit substrate 22 is effected by wire-bonding an electrode 5 on the sensing element 4 and a lead portion 111 formed on the control circuit substrate 22 together by a wire 8 such as tens to hundreds xcexcm of aluminum.
Thus, an output signal from the sensing element 4 in response to the air flow rate or air flow velocity flowing into the main conduit 20 can be led to the connector-connecting portion 104 through the control circuit substrate 22.
The electrode 5 of the sensing element 4 is connected with the lead portion 111 of the control circuit substrate 22 by wire bonding. It is generally done by first recognizing a predetermined position of the electrode 5 and the lead portion 111 by means of image recognition processing equipment before bonding them by an automatic bonder (automatic bonding machine). Both the electrode 5 of the sensing element 4 and the lead portion 111 on the control circuit substrate 22 are minute or microscopic. Therefore, workability and reliability of the wire bonding highly depend on how precisely their relative position is secured.
However, in such a structure as stated above, the sensing element 4 is disposed in the housing portion 109 of the support 108 by the adhesive agent and the control circuit substrate 22 is disposed on the base portion 110 by the adhesive agent. Thus, there are included two factors of variation to be generated when the sensing element 4 and the control circuit substrate 22 are assembled. Further, even if there is caused variation in each of application quantity of the adhesive agent, there is some possibility that the relative position of the electrode 5 and the lead portion 111 does not agree.
Therefore, in the electrode 5 or the lead portion 111, when the bonding position deviates from a predetermined range or deviates too much therefrom, it is necessary to correct the bonding position where the image recognition is completed, for resetting. Therefore, 44 lowering of the reliability of the bonding portion and deterioration of the yield percentage are easily caused and working efficiency is also lowered.
Further, the sensing element 4 is secured in the housing portion 109 of the support 108 by the adhesive agent, but it is the so-called cantilevered. Therefore, the sensing element 4 may be disposed in a recess or convex manner relative to the surface of the support 108 depending on the application condition of the adhesive agent. In this case, there is caused individual difference in a flowing manner of an intake air and it is easy to cause variation of detection accuracy.
It is therefore an object of the present invention to solve the above-mentioned problems and to provide stable bonding so as to improve the reliability of a bonding portion.
According to this invention, there is provided a holder for disposing a plate-like sensing element in a predetermined flow passage. The holder is provided with a housing portion for disposing the sensing element in a predetermined position. It has a rectification structure portion for rectifying the flow of an intake fluid and a connecting terminal securing portion embedding a connecting terminal for fetching a signal of the sensing element therein, wherein the rectification structure portion and the connecting terminal securing portion are integrally formed by insulating material.
Preferably, the connecting terminal is embedded in the connecting terminal securing portion so that the surface thereof is exposed.
In one preferred manner of this invention, the rectification structure portion is formed to have a round fin-plate shape or wing shape at least on the upstream side.
In a further preferred manner of this invention, there is provided, on the bottom surface of the housing portion, a positioning portion for controlling the height of disposition of the sensing element in its thickness direction of the sensing element so that the upper surface of the sensing element has the same height as the surface of the holder.
Preferably, positioning portions are provided in at least 3 places.
In a still further preferred manner of this invention, there is provided a metal member on the bottom surface of the housing portion and an adhesive agent is applied on the metal member to fixedly bond the sensing element thereon.
Advantageously, the metal member is formed to have a lead frame shape together with the connecting terminal of the same material as the metal member, and it is then integrally formed with the rectification structure portion and the connecting terminal securing portion so as to form the holder by removing an unwanted part therefrom.
Preferably, the connecting terminal has one end electrically connected to an electrode of the sensing element and the top of that one end is bent in the direction of the bottom surface of the holder to be embedded therein.
In a preferred manner of construction, the connecting terminal has one end electrically connected to the electrode of the sensing element, wherein the top of that one end is projectingly disposed to be gradually longer from the central portion to peripheral portion to surround the electrode of the sensing element.
Preferably, the electrode of the sensing element is disposed in an arch shape to allow the central part thereof to project longer than the peripheral part relative to one end of the connecting terminal that is electrically connected to the electrode.
Advantageously, the holder is obliquely disposed in a flow passage relative to the flow direction of a fluid, wherein the other end of the connecting terminal opposing to one end thereof that is connected to the electrode of the sensing element is extended to a control circuit substrate for controlling the sensing element, bent to be substantially parallel to a connecting terminal insertion opening that is linearly formed at the outer edge of the control circuit substrate and then inserted in the connecting terminal insertion opening for connection.
Preferably, the metal member is disposed on the bottom surface of the housing to cover a part of or all over the reverse side of the sensing element and a part of the metal member is connected to a power ground or an electromagnetic shielding member to form an electromagnetic shielding structure for insulating the electromagnetic noise radiated on the sensing element.
Advantageously, a recessed adhesive agent storage portion for storing the extruded adhesive agent is provided near a portion where the adhesive agent is applied to fixedly bond the sensing element in the housing portion of the holder.
Preferably, the adhesive agent storage portion is provided between a portion where the adhesive agent is applied and a diaphragm portion formed on the upper surface of the sensing element.
Advantageously, the adhesive agent storage portion is formed as a groove to cover the outer periphery of the portion where the adhesive agent is applied.
Preferably, an extension portion having a recessed step extended outward from the side of the sensing element is provided on the side of the housing portion to surround the portion where the adhesive agent is applied for fixedly bonding the sensing element.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.